The intensification of agriculture relies on the application of large quantities of phytosanitary products, which contaminate the air, soil, water, and risk human life. This study was carried out in the Gharb plain, which belongs to the Sebou watershed in the North-West of Morocco. The goal of this study is to evaluate the contamination of the groundwater by insecticides using liquid chromatography-tandem mass spectrometry (LC-MS/MS) and Gas Chromatography-Tandem Mass Spectrometry (GC-MS/MS) analyses. This research paper covers the analysis of 20 samples of 20 different wells for an irrigated perimeter of 250,000 ha of the surface. Further, the analyses show the presence of intense contamination caused by insecticides, which are concentrated in the southern part of the study area, where the contamination level is 50% of the water samples. This exceeds the norm of the World Health Organization (WHO) standard, which is represented in 0.5 µg/l. Furthermore, the analyses also detect the presence of 22 active ingredients of insecticides, such as malathion, methomyl alderine, dieldrin, and fenthion. Risk assessment in our studies allowed us to determine that the different RQ calculated for five insecticides (Malathion; Mythomil; chloropyrifos-ethyl; Diazinon) recorded in underground water were up to 1, which proves the intensive use of insecticide in this region and the high risk of contamination.